# RHBVS: ROSE SWE’s Heuristic Based Virus Scanner

ROSE SWE, Ralph Roth

    $Id: rhbvs.txt,v 1.138 2024/06/07 13:41:09 ralph Exp $
    Format: UTF8/ISO-8859-15, Windows CR/LF, English (UK), Written in ASCII-DOC

    __________  ___ _________________   _____________
    \______   \/   |   \______   \   \ /   /   _____/
     |       _/    ~    \    |  _/\   Y   /\_____  \
     |    |   \    Y    /    |   \ \     / /        \
     |____|_  /\___|_  /|______  /  \___/ /_______  /
            \/       \/        \/                 \/ ⓒ 𝓫𝔂 𝓡𝓞𝓢𝓔_𝓢𝓦𝓔

Behavior-based detection (also called "dynamic detection")

RHBVS, short for "ROSE SWE Heuristic-based Virus Scanner," is an anti-virus software that employs heuristics to detect malware. Heuristics are problem-solving strategies that rely on practical experience and general rules to find solutions. In the context of antivirus software, heuristics are utilized to identify malware by analyzing its behavior or characteristics, rather than relying solely on a database of known malware signatures.

The ROSE SWE heuristic-based virus scanner functions by scrutinizing the behavior of a program or file and comparing it against a collection of heuristics specifically designed to identify common patterns of malicious behavior. If the program or file exhibits behavior that aligns with one or more of these heuristics, it is flagged as potentially malicious.

Heuristic-based anti-virus software proves effective in detecting new or unidentified threats that have yet to be included in the database of known malware signatures. However, since heuristics are based on general rules, they can occasionally produce false positives, erroneously flagging benign programs or files as malicious.

To ensure robust protection against malware, it is crucial to utilize a comprehensive antivirus solution that incorporates multiple layers of defense, including signature-based detection, heuristics-based detection, and behavior-based detection. This multifaceted approach enhances the overall security posture and minimizes the risk of both known and emerging threats.

## 1. Introducing RHBVS

RHBVS is a DOS virus scanner for DOS file and hybrid viruses using heuristic scanning technologies and also signature-based detection! This means that RHBVS does not need to be regularly updated like a normal virus scanner. RHBVS also uses an intelligent code analyser. Detection modules for batch viruses, trojans, malware, scripting viruses such as Coral Draw, VBS, HTML, Windows Batch (WBT), JavaScript, SHS (Windows Shell Scrap), Powershell, Bash and IRC (Mirc) script worms are also included!

This is currently/was a unique feature - no other scanner can scan e.g. IRC, HTML or VBS worms with heuristics! RHBVS gives you a detailed virus analysis based on the built-in scan engine.

## 2. Why?

RHBVS was mainly written to be a test platform for the product VirScan Plus by ROSE SWE. All improvements done in VirScan Plus improves RHBVS, FindMirc and vice versa. For this reason RHBVS is limited in flexibility (e.g. checking boot sectors, Windows system memory or the MBR).

## 3. Requirements

- IBM compatible PC with a 80386 CPU and co-processor!

- 620 KB of free memory and DOS version 5.0 or higher or

- Windows 32 bit (RHBVS will not run under Windows 64 bit)

If you are interested in sponsoring the porting of RHBVS to Windows 64-bit or Linux, please reach out to us. While there are currently no plans for such a port due to perceived lack of demand and sponsors, we are open to considering it with sufficient support. In the meantime, we recommend utilizing MPScan (available for DOS32, Win32+64, Linux32+64), a multi-platform malware scanner that incorporates both heuristics and signature-based detection, and has comparable or even superior detection rates.

### 3.1. Terms

#### 3.1.1. Heuristic (computer science)

In computer science, a heuristic is a technique designed to solve a problem that ignores whether the solution can be proven to be correct, but which usually produces a good solution or solves a simpler problem that contains or intersects with the solution of the more complex problem.

Heuristics are intended to gain computational performance or conceptual simplicity potentially at the cost of accuracy or precision.

#### 3.1.2. Computer Virus

In computer security technology, a virus is a self replicating program that spreads by inserting copies of itself into other executable code or documents (for a complete definition: see below). Thus, a computer virus behaves in a way similar to a biological virus, which spreads by inserting itself into living cells. Extending the analogy, the insertion of the virus into a program is termed infection, and the infected file (or executable code that is not part of a file) is called a host. Viruses are one of the several types of malware or malicious software. In common parlance, the term virus is often extended to refer to computer worms and other sorts of malware. This can confuse computer users, since viruses in the narrow sense of the word are less common than they used to be, compared to other forms of malware such as worms. This confusion can have serious consequences, because it may lead to a focus on preventing one genre of malware over another, potentially leaving computers vulnerable to future damage. However, a basic rule is that computer viruses cannot directly damage hardware, only software is damaged directly. The software in the hardware however may be damaged.

While viruses can be intentionally destructive (for example, by destroying data), many other viruses are fairly benign or merely annoying. Some viruses have a delayed payload, which is sometimes called a bomb. For example, a virus might display a message on a specific day or wait until it has infected a certain number of hosts. A time bomb occurs during a particular date or time, and a logic bomb occurs when the user of a computer takes an action that triggers the bomb. However, the predominant negative effect of viruses is their uncontrolled self reproduction, which wastes or overwhelms computer resources.

Today (the trend started round 2005), viruses are somewhat less common due to the popularity of the Internet - instead malware, ransomware and Trojans meanwhile dominate.

Malware, short for malicious software, is an umbrella term used to refer to a variety of forms of hostile or intrusive software, including computer viruses, worms, Trojan horses, ransomware, spyware, adware, scareware, and other malicious programs. It can take the form of executable code, scripts, active content, and other software. Malware is defined by its malicious intent, acting against the requirements of the computer user and so does not include software that causes unintentional harm due to some deficiency (e.g. bugs).

## 4. Options and Switches

Please note that command line options in RHBVS are not case sensitive. You can use either the slash "/" or the hyphen "-" to indicate the start of an option. Additionally, options can be configured using the environment variable RHBVS.

    set RHBVS=...

To disable an option set by setting RHBVS=… you can use the "-" at the end of the option!

when you set

    set RHBVS=/all

than you can disable /all with

    rhbvs c: -all-

### 4.1. Command Line Options

Run RHBVS.EXE with

    /?  to see the current supported options.

Try also

    /?? or /UNDOC to see a list of the advance options.

You can scan as many drives and directories as you want per run.

    /vb Code Analyzer (past the switches /ANALYZE or /ANALYSE)

With this switch RHBVS gives you a detailed description of all the flags the heuristic scan engines have found.

You can use the option

    /vbk  then RHBVS waits for a key stroke after every analysis.

Use the additional option

    /log  to save the analysis into a log file.

### 4.2. The Option /virsort

A special note about this option.

| This is one of those "undocumented" switch RHBVS supports. With this switch you can sort in viruses AVP/FProt/VSP/DrSolly etc. misses. With this option RHBVS creates a log file suitable for Virsort or Zoo-Sort (utilities meanwhile deprecated). Take a look at the batch file RZOOSORT.BAT which is included in the package!

For more "undocumented" switches try also: rhbvs -??

## 5. User documentation

HINT: This text file is written in AsciiDoc and has been converted into a nice HTML file. German-speaking users should download the virus scanner "VirScan Plus" (VSPxxxx.*) and read the German documentation there for further understanding.

## 6. Virus classification

RHBVS classifies the different virus types, their code size and the behavior.

The classification has the following scheme:

    {Virkit:}[Main Class]{.Length{.Minor Class}{.Germs} (Flags)

    -=[ Virkit ]=----------------------------------------------

    Viruses created with a virus kit just like

    + Biological Warfare (BW)
    + DReg
    + Father_Mac
    + GOTH
    + IVP
    + NRLG, Nuke
    + PS-MPC, MPC, G2
    + TPE, MtE, GCAE, RTFM  etc.
    + VCC
    + VCL
    + VLAD

    -=[ Main Class ]=------------------------------------------

    + Backdoor- Backdoor (Trojan)
    + Bat     - DOS Batch file virus or Trojan
    + Boot    - Boot virus and EXE header infector
    + CSC     - Coral script virus
    + Companion - small companion viruses
    + Crypt   - encrypted virus
    + Fast    - fast infector, like Dark Avenger
    + File    - appending file infector
    + HLLx    - High level language viruses
                x stands for C=companion, O=overwriting, and P=parasitic
    + IIS     - MS Internet Information Server Worm
    + Joke    - Joke/Fun program. This is not a virus.
    + JS      - Java script virus
    + Mini    - larger overwriting file infector
    + MIRC    - MIRC script worm
    + Multi   - Hybrid (multipartite) files and boot infector
    + Poly    - Polymorphic encrypted virus
    + PIRC    - PIRC script worm
    + SillyR  - trivial memory resident file infector
    + Stealth - virus with stealth capabilities (size or file stealth)
    + TSR     - virus stays resident in memory
    + Tiny    - trivial appending file infector (e.g. Danish)
    + Trivial - overwriting file infector (e.g. Trivial.45)
    + WBT     - Windows Batch virus
    + VBS     - Visual Basic Scripting virus
    + VBS+VBS - multiple VBS infections of one host - yes RHBVS can
                detect multiple infections!
    + Win32,  - Windows platform specific virus or Trojan
    + Win95,98

    + exact virus name, when using the switch /TROJ
    + exact virus name if found by the polymorph decryption engine
      (Hare, MtE, BW, Grief, TPE, Lucky.Gott etc.)

    -=[ Length ]=----------------------------------------------

If possible the virus size. If there is a question mark (e.g.) Virusname.438? the code analyzer assumes this as the virus size!

    -=[ Germs ]=-----------------------------------------------

If it is a Generation-1 sample.

    -=[ Flags ]=-----------------------------------------------

RHBVS uses the following flags as short cuts:

    A - Anti debugging or anti heuristic code is used
    B - can overwrite the boot sector/MBR (used by the payload or
        by a boot sector infector)
    D - found a decryption routine (virus seems to be encrypted)
    E - Infects EXE headers like Headerbug or Pure
    F - suspicious file access
    H - uses hardware related instructions - common for boot viruses
    I - uses INT 21h calls in a suspicious way
    M - memory resident. Code will remain resident or will control
        some of the DOS functions. Typical for resident file infector
    O - opens files for writing code into it
    R - suspicious relocation code, typical for file infector
    T - checks the date or time (usually used for a payload etc.)
    U - Virus tries to stay resident in UMB (upper memory blocks)
    W - Windows malware or windows shell code

    ! - uses at least FCB and/or directory stealth methods
    # - is encrypted or uses code to confuse a code analyzer

    Flags will be "compressed" if more than three flags were found.
    RHBVS will show them as "flag: number of occurrence", e.g.: R:4

### 6.1. Some terms

In computer terminology, polymorphic code is code that mutates while keeping the original algorithm intact.

Polymorphic code was invented in 1992 by the Bulgarian cracker Dark Avenger (a pseudonym) as a means of avoiding pattern recognition from anti virus software. This technique is sometimes used by computer viruses, shell code exploits and computer worms to hide their presence. Most anti virus software and intrusion detection systems attempt to locate malicious code by searching through computer files and data packets sent over a computer network. If the security software finds patterns that correspond to known computer viruses or worms, it takes appropriate steps to neutralize the threat. Polymorphic algorithms make it difficult for such software to locate the offending code as it constantly mutates.

Encryption is the most commonly used method to achieve polymorphism in code. However, not the entire code can be encrypted, as it would be completely unusable. A small part of it remains unencrypted and is used for the first start and to decrypt the encrypted software. Anti-virus software targets this small unencrypted part of the code.

Malicious programmers have tried to protect their encrypted code from this strategy by rewriting the unencrypted decryption engine each time the virus or worm is spread. Sophisticated pattern analysis is used by antivirus software to find the underlying patterns in the various mutations of the decryption engine in the hope of reliably detecting such malware.

Stealth: Some viruses try to fool anti virus software by intercepting its requests to the operating system. A virus can hide itself by ensuring that a request of anti virus software to read an infected file is passed to the virus, instead of to the operating system. The virus can then return an uninfected version of the file to the antivirus software, so that it seems that the file is "clean". Modern anti virus software employs various techniques to counter stealth mechanisms of viruses. The only completely reliable method to avoid stealth is to boot from a medium that is known to be clean.

## 7. False Positives

A false positive, also referred to as a false alarm, occurs when a test erroneously indicates the presence of a signal when there is none. False positives can be encountered in various detection algorithms. For instance, in optical character recognition (OCR), the algorithm may identify an a even when there are only a few dots resembling the letter.

When developing such software, there is always a trade-off between false positives and false negatives, where a true match is not detected. This trade-off involves balancing the risk of Type I errors (false positives that wrongly reject the null hypothesis) against Type II errors (false negatives that fail to reject the null hypothesis when it is false) in statistical hypothesis testing.

Typically, there is a predetermined threshold that determines how closely a match should resemble a given sample before the algorithm reports it as a match. By increasing this threshold, the algorithm becomes more stringent in its detection, requiring a closer similarity for an object to be flagged, thus reducing the occurrence of false positives.

As RHBVS is a rules-based heuristic virus scanner, encountering false positives is a normal part of its operation. If you come across false positives, you can send the executable file for verification and improvement of the scanner. It is important to note that on standard installations, RHBVS should not trigger any false positives.

### 7.1. Known False Positives

Currently RHBVS detects some hacking tools like unHS etc. But no normal user has this stuff on the disk drive - so no action is taken to fix it. Other known false positives are the memory resident anti-virus programs TBAV and FProt. Both are now obsolete and no longer available.

RHBVS flags them as:

    "D:\WINDOWS\TBAV_WIN\TBSCANX.EXE  Fast.TSR.File (MBIBBMFR)"

This means code to stay resident and to intercept file operation like opening or execution of executable files. When looking at the code analyser of RHBVS we see that TBSCANX stays memory resident (M- flags+TSR),

INT 21h sub functions 3D, 3E & 6C which is typical for a fast infector (Fast) and INT 13h sub function 02 which is typical for boot viruses (B- flags). Due to the fact TBSCANX stays resident it relocates (R-flags) to get its address.

| THAT’S ABSOLUTELY RIGHT - SO RHBVS ONLY REPORTS A PROGRAM LOOKING LIKE A STANDARD FILE VIRUS…. :))

### 7.2. False positives causes by third party software

Ralf Borgmann reported that the DSAV.VxD intercept the "Live Bait Test" and reports an unknown virus. This is a bug and false positive of the DSAV.VxD - it can be reproduced only by the first start of RHBVS :-))

    >>>>>>> Please send me also viruses RHBVS misses. <<<<<<<<<<

## 8. Error Codes

RHBVS uses the following DOS return codes when terminating. You can use them in batch files or tools like Skull Check etc.

    Error level |   Meaning
    ------------+-------------------------------------------------
        0       |   RHBVS completed without any error and without
                |   finding any suspicious program!
        1       |   Misc. errors, like video mode or DOS version!
        2       |   The help screen was invoked.
        3       |   A virus was found in memory (by Quick Memory Scan)
        4       |   One of the signatures files (RHBVS.SIG or
                |   VIRSCAN.TRJ) is damaged or the access is denied!
        5       |   An error occurred creating the log file (/LOG=).
        6       |   Not used
        7       |   Path specified to scan: Access denied
        8       |   Insufficient memory/not enough memory
        9       |   VirScan.IRC|VirScan.VBS is missing or corrupt
       10       |   One or more suspicious files have been found!
     11..18     |   DOS error, please report it to ROSE SWE!
       xx       |   Internal error, please report it to ROSE SWE!

## 9. Technology

RHBVS currently uses over 350 modules to detect the various types of computer viruses. RHBVS can also emulate and follow a polymorphic hidden jump to the virus body, for example used in the Nostradamus.3584 (a.k.a. Grief) viruses. All the software modules have been taken from ROSE SWE’s VirScan Plus virus scanner.

RHBVS skips files smaller than 32 bytes. The scanner can even detect and emulate anti-heuristic programmed code! RHBVS has a detection rate of over 98% for trivial and mini viruses and over 80% for boot (image files) and hybrid viruses.

The overall detection is (tested on my virus collection):

       Version [Samples]   0.01          0.10           1.00 /TROJ
    --[Percent]-------------------------------------------------------
    ITW-Test set Germany   30.1 [412]    36.9 [412]     39.3 [412]
    Classified viruses(1)  N/A           64.1 [6037]    66.7 [6119]
    Unclassified viruses   22.4 [1867]   27.5 [1867]    29.5 [2020]
    ------------------------------------------------------------------

       Version [Samples]   1.03 (1)      1.05 (1)       1.07 (1)
    --[Percent]-------------------------------------------------------
    ITW                    60.4 [379]    60.4 [379]     66.8 [373]
    Classified(1)          77.7 [????]   77.3 [6808]    77.9 [8122]
    Unclassified(2)        44.1 [2007]   45.6 [2371]    41.0 [1289]
    ------------------------------------------------------------------

       Version [Samples]   2.00 (1)      2.02 (1)       2.03 (1)
    --[Percent]-------------------------------------------------------
    ITW                    75.3 [402]    80.8 [647]     80.9 [649]
    Classified(1)          82.1 [8122]   84.0 [9284]    84.4 [9215]
    Unclassified(2)        45.3 [1289]   48.8 [1296]    49.6 [1203]
    ------------------------------------------------------------------

       Version [Samples]   2.04 (1)      2.05  (1)      2.10 (1)
    --[Percent]-------------------------------------------------------
    ITW(3)                 81.2 [649]    84.8 [649]     76.3 [2503]
    Classified(1)          84.6 [9301]   85.9 [9408]    85.1 [9553]
    Unclassified(2)        48.2 [1480]   50.1 [2532]    49.4 [1042]
    ------------------------------------------------------------------

       Version [Samples]   2.11 (1)      2.20 (1)       2.22 (1)
    --[Percent]-------------------------------------------------------
    ITW(3)                 84.1 [649]    76.3 [2503]    85.8 [649]
    Classified(1)          84.6 [9301]   85.3 [10181]   79.2 [12409]
    Unclassified(2)        42.8 [998]    42.4 [1962]    55.3 [978]
    ------------------------------------------------------------------

       Version [Samples]   2.30 (4)      2.35
    --[Percent]-------------------------------------------------------
    ITW(3)                 86.2 [1718]
    Classified(1)          76.4 [18329]
    Unclassified(2)        84.5 [1438]   86.8 [795]
    MIRC scripts          100.0 [1018]  100.0 [1082]
    ------------------------------------------------------------------

       Version [Samples]    2.50 (July 1999)        3.01 (Jan 2000)
    --[Percent]-------------------------------------------------------
    FProt, unique(1)        75.8 [19236/25393]
    Unclassified(2)         72.1 [546/757]          88.2 [1871/2122]
    AVP, unique             70.2 [10392/14801]      65.1 [9789/15057]
    Scripts (IRC, VBS, JS) 100.0 [1233/1233]
    ------------------------------------------------------------------

(1) Detectable by F-Prot (includes more than 700 HLL viruses & Trojans!) All viruses are unique (Virsort)!

(2) These are REAL viruses in my incoming directories, which are not scannable by the newest KAV and F-Prot versions!!!

(3) ITW test set based on Joe Wells ITW lists. Included are all ITW file and boot infector Some viruses used by the VTC ITW test bed has been added to the RHBVS ITW test bed as well as some RIMC viruses.

(4) With switches /TROJ and /HIGH

Main goal is to increase the overall detection rate as well as reduce the false positives.

## 10. Bugs & Limits, Future

- Currently RHBVS runs only on DOS environments. Please provide feedback if we should port RHBVS to Windows and Linux. The trade-off of the port will be around 20-30% less detection (non-portable assembler routines used). Please have a look at MPSCan that is a similar portable heuristic scanner for multiple platforms.

- This program can only handle file names with a maximum of 67+12 chars length (including paths) because the MS-DOS box of NT. If you have longer file names (Win95/98/NT: supports IMHO 252 chars) then you have to map your paths. Detection has been added for LAN-Manager, Netware based networks and Microsoft compatible networks.

- RHBVS is currently not able to scan inside archives (ARJ, ZIP, LHA etc.) as well as macro and boot viruses!

- RHBVS cannot run under some debuggers like Soft Ice due to the HackStop security envelope. ;-)

- RHBVS is limited in scanning MS Office documents, boot viruses as well as Win32 executable (PE/NE).

- RHBVS cannot run under some debuggers like Soft Ice due to the HackStop security envelope. ;-)

Testing a virus scanner is not an easy task and should be only done by experts on a large virus collection!

Suggested Options for Testing

- File viruses

      rhbvs <path> /all /high /log=c:\temp\vtc.log
                   /trj is default

- Boot viruses (on disks/bootable mediums)

RHBVS is not designed to scan for (old DOS) boot viruses. Use for that task VirScan Plus or the heuristic boot virus checker ChkPc.

## 11. License

Please note the following: RHBVS is distributed as AnyWare, which implies that the program and documentation are fully copyrighted by the author (ROSE SWE). The program is freely available for use in non-commercial environments, similar to freeware. If you find RHBVS beneficial and would like to contribute to its improvement, please feel free to send anything, for example helpful suggestions, such as emails, bug reports, or even monetary support to the designated contact. Your support is greatly appreciated!

## 12. History

### 12.1. Version 6

    07.06.2024  6.70        Maintenance update. Small enhancements,
                            new viruses added.

    12.03.2024  6.58        Maintenance update

    04.02.2024  6.47        Improved entry point engine. Maintenance update.
                            Small enhancements, new viruses added.

    27.12.2023  6.39        Better detection. New viruses added.

    30.11.2023  6.32        Better VCL detection.
                            Small enhancements, new viruses added.

    10.11.2023  6.26        Small enhancements, new viruses added.

    13.10.2023  6.19        AVR_Mini/Trojan.  Maintenance update.
                            Small enhancements, new viruses added.

    25.09.2023  6.18        Small enhancements, new viruses added.
                            Maintenance update.

    28.08.2023  6.17        Maintenance update adding new virus detection

    13.07.2023  6.16        Small enhancements around the AVR-Trivial engine.
                            New viruses added.

    20.06.2023  6.15        Maintenance update adding new virus detection

    05.06.2023  6.14        Maintenance update adding new virus detection

    06.05.2023  6.13        Maintenance update adding new virus detection

    08.04.2023  6.12        Maintenance update adding new virus detection

    23.02.2023  6.11        Maintenance update adding new virus detection

    07.02.2023  6.10        Added new *NIX script and batch detection
                            engine to RHBVS with more than 1000 viruses.

    31.01.2023  6.00        Rewritten IRC and Batchvirus engine. New viruses.
                            Improved entry point engine.

### 12.2. Version 5

    13.01.2023  5.71        Complete rewritten command line engine.
                            New viruses added. Improved entry point engine.

    15.12.2022  5.68        Enhanced AVR:Mini, AVR:Trivial & AVR:Silly
                            engines. Enhanced VirusKit detection. New
                            viruses added.

    25.11.2022  5.67        Enhanced AVR modules, new viruses added.

    09.11.2022  5.66        No user visible changes. Enhanced code emulation
                            and entry point detection. New viruses added.

    01.10.2022  5.65        Added 4 new AVR modules. New viruses added.

    11.09.2022  5.64        Small improvements and new viruses added

    02.09.2022  5.63        Version bump after adding a lot of new virus
                            signatures.

    25.05.2022  5.62        Fixes with UTF-8 formatting. Thus maybe 3rd
                            party scripts may be adjusted filtering the
                            output of RHBVS log file. New viruses added.

    15.05.2022  5.61        Small improvements. New viruses added.

    18.03.2022  5.60        Changes and enhancements to the internal
                            scan engine. Added new viruses.

    10.02.2022  5.54        Internal changes and improvements. Added new
                            heuristic signatures and malware detection.

    23.01.2022  5.52        Added a new AVR engine for DOS Debug script
                            viruses. Added new viruses.

    07.12.2021  5.51        New viruses added

    09.07.2021  5.50        Internal changes and optimization for the virus
                            databases. Better and faster detection.
                            New viruses added.

    24.06.2021  5.40        Internal enhancements. Added new viruses.
                            RHBVS now checks for import files using the file
                            rhbvs.cfg. All files from rhbvs.cfg must be
                            provided.

    08.06.2021  5.32        New viruses added. Changed internal database
                            format (virscan.*)

    25.05.2021  5.31        New viruses mainly from MPScan added. Small
                            enhancements.

    06.03.2021  5.30        Added the detection engine from MPScan to RHBVS.

    22.02.2021  5.22        More viruses added.

    12.02.2021  5.21        Fixed a few false positives. Added new viruses.

    14.01.2021  5.20        Rewritten "MalwareScriptViruses" engine, therefore
                            all virus databases require the internal version
                            4.00 or higher. New viruses added.

    29.10.2020  5.15        Added more than 700 viruses. Updated the AVR
                            Modules again. Added more signatures for boot
                            and multipartite viruses.

    16.10.2020  5.14        Added around 300 viruses. Changes around the
                            AVR modules (Tiny, Trivial, Mini). Enhanced
                            documentation.

    13.10.2020  5.13        Added around 400 viruses. Changes around the
                            AVR modules.

    05.10.2020  5.12        Massive changes and enhancements around the AVR
                            modules. Added hundreds of viruses.

    19.09.2020  5.11        New viruses. Added 4 new heuristic search modules

    01.09.2020  5.10        Added new viruses.

    01.07.2020  5.09        Added new viruses.

    27.03.2020  5.08        Added new viruses.

    08.12.2019  5.07        Added new viruses. More heuristic detection.

    01.11.2019  5.06        Some internal changes. Added new viruses.

    22.06.2019  5.05        Added new viruses. Documentation update.

    29.12.2018  5.04        Added new viruses. Documentation update.

    20.09.2018  5.03        Added 22.000 viruses.

    28.03.2018  5.02        This documentation was ported to AsciiDoc.

    06.12.2017  5.01        Small enhancements. Major reprogramming
                            of the signature based detection.

    29.11.2017  5.00        Trojan detection is not compatible with pre
                            5.00 releases. New viruses detection added.

### 12.3. Version 4

    27.11.2017  4.98        Public release with new viruses detection.

    09.09.2017  4.97        Public release. Enhancements and new viruses.

    15.02.2017  4.96        Enhancements and new viruses.

    22.04.2016  4.93        Public release. Enhancements and new viruses.

    20.04.2015  4.92        Public release. Enhancements and new viruses.

    10.11.2014  4.91        Public release. Enhancements and new viruses.

    30.12.2013  4.90        Generic encrypted script detection added.
                            Enhancements and new viruses.

    30.10.2013  4.84        Enhancements for better detecting Win32 and
                            Win64 viruses. Added new viruses.

    03.03.2013  4.83        5000 viruses added, changed home page URL

    30.09.2012  4.81        Small enhancements, new viruses.

    16.10.2011  4.80        New viruses added, esp. the German
                            "Staatstrojaner" (file+live test).

    07.06.2011  4.79        New viruses added. Enhancements for Win32,
                            Dos32 and Linux console output.

    03.02.2011  4.78        New virus detection added. Fixed an
                            run-time error bug.

    13.08.2010  4.77        Added a lot of windows malware and
                            windows shellcode detection stuff.
                            New viruses added.

    18.06.2010  4.76        Win32.Shellcode handler improved.
                            VBS encrypted detection improved.

    13.04.2010  4.75        New viruses added. New icon for RHBVS.
                            Documentation updated.

    19.03.2010              Major update/enhancements added to PeHead.

    14.03.2010  4.73/4.74   Small enhancements and new viruses added.

    19.02.2010  4.70-4.72   Small bug fixes and enhancements. New
                            viruses added.

    30.03.2009  4.68/4.69   Massive enhancements around the /rename
                            function. Bug fixes and new viruses added.

    06.02.2009  4.67        Small enhancements for Windows Vista.
                            New viruses added.

    16.11.2008  4.66        Small bug fixes and enhancements. New
                            viruses added.

    11.01.2007  4.65        Changes on the /Rename functions.

    30.09.2006  4.64        Enhancements, new viruses. Changed
                            virus database.

    09.08.2006  4.63        Small enhancements (e.g. .PNG detection).

    25.04.2005  4.62        Enhanced the docs. Added new signatures
                            to the heuristic scan engines.

    10.03.2005  4.60        Changed and enhanced the internal database.
                            Added new scan engines and viruses.

    06.01.2005  4.51        Enhanced VBS engine. New viruses added.

    13.11.2004  4.50        Added new viruses.

    19.08.2004  4.50-RC2    Added ~600 new viruses. Fixed a few
                            false positives.

    17.08.2004  4.50-RC1    Complete redesign of the script scanning
                            engines (VBS, Script, IRC, Batch etc.).
                            A lot of new viruses added.
                            The signature files (virscan.*) are not
                            compatible with the 4.1x and below
                            releases!

    16.06.2004  4.13        Small fixes, 400 viruses added.

    14.04.2004  4.12        Added QWTC - "Quick Windows Trojan Check"

    21.01.2004  4.11        Bug fixing of the command line handling
                            engine. New viruses added.

    09.09.2003  4.10        Bug fixing, RHBVS now requires a
                            co-processor.

    07.09.2003  4.05        Added and enhanced some scan engines
                            and added tons of new viruses. Bug fixes.
                            (EXE file is therefore 20 KB bigger!).

    06.09.2003  4.02        Ported and enhanced some of the scan
                            engines to Linux. New viruses added.

    16.07.2003  4.00        New viruses. Changed the internal Trojan
                            and malware engine to run on Linux too.

### 12.4. Version 3

    13.05.2003  3.96        Added tons of new viruses.

    25.03.2003  3.95        New and enhanced engines for VBS viruses.

    27.02.2003  3.94        Fixes for HMA/A20 gate check. Added tons
                            of new viruses.

    07.11.2002  3.93        Added tons of new viruses.

    05.11.2002  3.92        Added new viruses, therefore internal hash
                           tables had to be adjusted.

    03.11.2002  3.91        Build 433
    20.08.2002  3.91        Build 423
    18.06.2002  3.91        Documented the switch /OnlyFull. Added
                            new viruses.

    05.05.2002  3.90        New viruses added. Changed the format of
                            Virscan.trj

    25.04.2002  3.81        Added new viruses. Fixed a false positive.
    23.04.2002  3.80        Fixed a bug with Win2000/NT. Changed the
                            signature files.

    19.04.2002  3.73        Added 120 viruses.
    11.04.2002  3.72        Added 300 viruses.

    17.03.2002  3.71        Changed documentation (also renamed from
                            *.DOC to *.TXT). Added new viruses.

    22.01.2002  3.70        New viruses. DOCS changed. Bundled with Win32
                            installer.

    09.01.2002  3.64        New viruses. Added .PIF file for Win9x.

    10.12.2001  3.63        New viruses added. New option -delYN added.

    08.10.2001  3.62        New viruses added.

    15.08.2001  3.61        New viruses. New generic scan engine for
                            IIS-Worms added. Should find every worm
                            that uses the IIS Backdoor. To scan for
                            such worms, you currently need the option -ALL

    30.07.2001  3.60        Added 300 new batch and script viruses
                            using the new designed scan engines from
                            RHBVS 3.55. Those signatures are stored
                            in the new file "VIRSCAN.IRC".

    26.07.2001  3.55        Added tons of new viruses. Added .LNK as
                            default extension. Introduced a version
                            numbering to VIRSCAN.VBS (needed for new
                            generic script detection). Added generic
                            script detection engine. Added new engines.

    08.06.2001  3.51        New viruses added. Better detection of
                            anti heuristic programmed VBS viruses.

    03.05.2001  3.50        Depending on your machine (386, 486 etc.)
                            and operating system, RHBVS is now up to
                            20 percent faster. New viruses.

    16.03.2001  3.45        Added more than 100 new VBS viruses. Added
                            .JSE, .VBE, .WSH as a default extension.
                            Included on the fly decryption of MS VBS
                            encrypted files (.VBE). New signatures
                            added. VBS scan engine updated.

    17.02.2001  3.41        Update of the VBS scan engine to find
                            VBS.NeueTarife/AnnaKov. New viruses.

    19.01.2001  3.40        New viruses added (of course :). Option
                            -ShowErr added. Statistic enhanced
                            (+ time, + total errors). Some false
                            positives fixed. We have ported parts of
                            the scan engines to win32. As a benefit
                            the scanning is now much faster
                            due to the enhancements we had to do for
                            the porting.

    04.01.2001  3.32        Added four new scan engines, VBS engine
                            was enhanced. 70 new viruses added.

    27.11.2000  3.31        New viruses added.

    14.09.2000  3.30        Added Win32 Stealth Bait test. New
                            viruses added.

    25.07.2000  3.21        Added .VBA as default extension. /RenPE
                            enhanced. New viruses added.

    05.07.2000  3.20        Faster scanning due to rewrite of the VBS
                            and MIRC analyzer Add option /NoScript
                            (same as /NoVBS). New viruses. Added 180
                            Trojans. Added MS Mail scanning (MSFT).
                            Added generic VBS detection (construction
                            kits etc.). Added generic Batch file
                            detection.

    22.06.2000  3.11        Added detection for 680 Backdoors. 20 new
                            VBS viruses added. Added .VXD and .SHS as
                            default extensions. Added 70 Trojans. SHS
                            will now be scanned too (VBS.Life_Stages).

    26.05.2000  3.10        Added detection for 250 Win/Win32 Trojans,
                            Backdoor and password stealing programs.
                            Added detection for 20 new VBS viruses.
                            Added .DLL extension as default. New viruses.

    07.05.2000  3.03        Due to the various VBS.Love-Letter variants
                            we added to the virus name additionally the
                            length. When you use RZOOSORT.BAT to sort
                            your Love-Letter variants, they go now in
                            separate directories.

    28.04.2000  3.02        Added MIRC detection in .PIF files. Added
                            option /NoVBS. /NoVBS is also set if
                            VIRSCAN.VBS was not found! New viruses :)
                            Added options /NoTrj and /NoTroj

    29.01.2000  3.01        Added HLP, AVI, CHM, FTS, CNT detection.
                            Added Joke class to RHBVS. New viruses :)
                            Changed the VBS detection engine for the
                            first anti RHBVS specific viruses.

    03.12.1999  3.00        Added ACE and (WAV) Wave detection. Added
                            "T" flag (time/date). Added 750 new viruses.
                            Added new scan engines. Added the options
                            /VB, /VBK (code analyzer) and /REPORT.
                            Better Java script detection added. Nicer
                            screen output. The switch /stdout is now
                            obsolete and not supported any longer!

### 12.5. Version 2

    01.09.99  2.56          Added ARJ and LZH archive detection.
                            Renamed /ANALYSE to /WHOLE (planed to
                            add switch /ANALYSE[=language.dat]).
                            RHBVS can now handle multiple infections of
                            VBS viruses.

    11.08.99  2.54          New viruses. Tested RHBVS under Win2000b3
                            Server and fixed all bugs.

    24.07.99  2.52          Added new VBS, JS and MIRC viruses using a
                            new detection engine.

    18.07.99  2.51          WBT (Windows Batch) virus class added.
                            New viruses added.

    10.07.99  2.50          HTML, JS, CS and VBS detection added. New
                            viruses and other malware added.

    24.05.99  2.35          Approx. 500 viruses added. Basic PIRC, INF
                            and VBS detection added. Option /COMP
                            (generic companion detection) added.

    17.02.99  2.34          Option /NOMEM added. New viruses.
                            Added detection of HTML, PDF (Adobe Acrobat)
                            and MDB (MS Access) file format.

    15.01.99  2.33          Option /RAW added. Bug with long directories
                            under Win-NT fixed. Tons of new viruses and
                            Trojans added. Added Natas decryption engine
                            from VSP. Enhanced the rhbvscum.awk script.

    02.01.99  2.32          Command line handling improved. Mirc detection
                            improved. Code analyser and option /Virsort
                            enhanced. New viruses and Trojans added.
                            File sharing handling for Windows enhanced.

    29.12.98  2.31          Fixed some bugs and false positives.
                            Enhanced the Mirc classification. Added
                            the rhbvscum.awk script to the package.

    29.11.98  2.30          Added Mirc script worm detection and
                            heuristics. Improved file handling.
                            Improved /RENAME capabilities. New viruses
                            and Trojans If VIRSCAN.TRJ is found
                            automatically option /TROJ is added!

    20.10.98  2.24/2.25     Non public releases!

    24.08.98  2.23          New viruses and Trojans Added a new
                            Trojan detection. Added new entry point
                            detection. Bug fixes. RHBVS uses now the
                            same "smart renaming" engine like RFW.
                            SYS virus detection added.

    17.05.98  2.22          New viruses. Added new scan engines (VCL,
                            Mini, Trivial etc.).

    07.04.98  2.21          Fixed a lot of minor bugs in the /Rename
                            section. Better Live Bait Test. RZOOSort
                            changed. Added a new internal scan engine.
                            Tons of new viruses added :)

    18.03.98  2.20          /Rename, /Renumber now support more Excel
                            formats (.XLA, .XLS etc.), credits: A. Marx
                            Added advanced check for resident stealth
                            viruses (Stealth Live Bait Test). Added
                            more than 40 boot viruses and more than
                            70 file infector Improved the boot
                            heuristics. Minor bug fixes.
                            Currently I am working on a neural network
                            for RHBVS so it many take a time for the
                            next release :-))

    15.02.98  2.11          Added or fixed the following features:
                            + Added more than 50 new viruses.
                            + Fixed some false positives (R. Borgmann)
                            + More compatible file access. Credits
                              (Christian Ghisler & Ralf Borgmann).
                            + Added new search engines and flags.
                            + RHBVS can now only be aborted with the
                              Escape key (SR by R. Borgmann).
                            + Heuristic flag compression/sorting
                            + /Renumber=Value switch now works
                              correctly (one of those undocumented
                              features :-))

    29.01.98  2.10          Enhanced check for stealth viruses and
                            fast infector added. Added 350 new
                            viruses. Enhanced companion detection.
                            Enhanced boot virus detection. Added new
                            search engines. Improved the statistics.
                            Enhanced code analyser Fixed some false
                            positives. Added the batch file
                            RZOOSORT.BAT to the package. RHBVS does
                            now a much better classification of the
                            virus using his new code analyser.
                            Changed the heuristic to produce less
                            false positives than the 2.05 release.

    28.12.97  2.04          Now the /LOG switch supports file names,
                            e.g. /LOG=C:\TMP\RHBVS.NEW etc. Changed
                            the error level (DOS return codes) and
                            documented them in RHBVS.DOC. New viruses
                            added, fixed some false positives and
                            bugs. New flag "A" added. Added the new
                            virus group "Poly". Added an entry point
                            resolver for the _310 virus. AVR for
                            boot viruses enhanced and improved.
                            Sanity (integrity) self check added!

    13.12.97  2.03          Fixed again some false positives received
                            from Ralf Borgmann. About 230 new viruses
                            added. Now the signatures file RHBVS.SIG
                            also contains flags. Added new search
                            engines. Modified the live bait test to
                            fool the DSAV.VxD.

    21.11.97  2.02          Fixed about 10 false positives (credits
                            Ralf Borgmann). Added new search engines
                            and new viruses. Overall detection ratio
                            is now 84 percent!

    08.11.97  2.01          Fixed two false positives. Added more than
                            20 new scan engines. Enhanced the Mini
                            and Trivial scan engine. Added more than
                            200 viruses! RHBVS now scans also files
                            with the extensions .IMG, .BOT and .BIN.

    01.11.97  2.00          Added the option /LOG to generate a
                            simple log file.
                            Added more than 80 new scan engines -
                            they are the compressed and optimized
                            search strings from VirScan Plus.

### 12.6. Version 1

    12.10.97  1.07          Added new viruses. Added a new entry
                            point detection for the _1015 virus.

    20.09.97  1.06          Windows NT compatibility enhanced. Added
                            new viruses.

    09.08.97  1.05          Added some viruses and a new entry point
                            detection engine for the Demo Fraud virus.
                            Windows-NT compatibility enhanced. Added
                            a PIF file for Windows NT 4.0.

    13.07.97  1.04          Added the switch /FILETYPE. Added a check
                            for corrupted files. Added a few new
                            viruses. Fixed some false positives.

    06.07.97  1.03          Enhanced the Mini-AVR module. Added new
                            viruses. Fixed some minor bugs. Added
                            option /HEUR.  Release for SAC ftp etc.

    28.06.97  1.02          Fixed two false positives. Added a few
                            viruses. Changed the help screen.
                            Added one search engine for EXE-Header
                            viruses. Changed access mode for faster
                            accessing write protected discs. Added
                            the 'E'-Flag.

    11.06.97  1.01virnet    Changed some DOCS. Release for Virnet.
    09.06.97  1.01          Added the Option /CONT and /HIGH.
                            Enhanced one search engine to find the
                            Make2 virus.

    07.06.97  1.00          Added the option /TROJ.
                            Improved the Tiny code analyser, added the
                            flags 'H' and '#'.
                            First official release

### 12.7. Beta Versions

    29.05.97  0.10          Improved the detection rate more than 5%!

    27.05.97  0.02          Added the option /AUTO and /BEEP.
                            Added RHBVSGER.FAQ, enhanced the DOC.
                            Fixed a bug when redirecting the output
                            using the stdout option (rhbvs -stdout>file)
                            Detection on exe packers added.

    22.05.97  0.01          Initial release

## 13. Credits

People who helped to improve this product or have given feedback.

| In alphabetical order

    Andreas Haak            code analyser & more
    Andreas Marx            technical consultant :)
    Axel Pettinger          Mirc stuff
    Bert De Rijck           Fam_????
    Carsten Kruse           Mr. "enhancements"
    Christian Ghisler       technical consultant :)
    Claus Vogt
    Frank Ziemann           Backdoor, Trojan and Worm testing
    Hanno Boeck             Mr. "false positives" :)
    Jerry Hodges            CRC32
    Joe Hartmann            Mirc, false positives, RIMC project
    Joerg Abdinghoff        initial idea for /ANALYZE, now /vb or /vbk
    Lukas-Fabian Moser
    Laurent Gerard          new virus
    Mano Schwarz
    Mathias Brunner
    Masterball/codeBreaker  HMA/A20 testing
    Michael Hering          checksum, FP, RHBVS.DOC, easily switches
    Nobert Kirch            stdout bug
    Peter Kosinar           FP, missed viruses
    Ralf Borgmann           Mr. RHBVS beta tester :)
    Robert Flogaus-Faust
    Sebastian Boehm
    Stonehead               Mr. "false positives" :)
    Tjark Auerbach          DOX
    Toralv Dirro            RIMC project
    Valentino Tosatti       Mr. "false positives" :)
    Veit Kannegieser

You? ..

## 14. Files

    CRCHECK.TXT    checksum file of the whole distribution
    ROSEBBS.TXT    the author's address and ROSE support BBS, WWW etc.

    FILE_ID.DIZ    short description of the package
      RHBVS.XXX    checksum file for integrity check
      RHBVS.MSG    Message/language file for switch /vb
      RHBVS.DOC    this documentation
      RHBVS.EXE    the main executable
      RHBVS.PIF    Win 3.1/9x/NT/2000 program interface file :-))

      RHBVS.SIG    some heuristic scan engines and flags
    VIRSCAN.TRJ    signature file for HLL viruses and Trojans
    VIRSCAN.IRC    signature file for script and batch viruses (IRC, BAT...)
    VIRSCAN.WSM    signature file for script viruses (IRC, VBS, JS, CSC...)
                   [windows scripting malware]
    VIRSCAN.MPV    signature file for multipartite DOS file viruses and
                   boot/MBR viruses. Contains also signatures for file viruses

    RHBVSCUM.AWK    AWK script to create statistics reports from RHBVS.LOG
    RZOOSORT.BAT    handy batch file to sort your unknown viruses!

## 15. Miscellaneous

Why is RHBVS.EXE such a small program? Well it is compressed using a so called online compressor. Here are the results finding the best compressor for RHBVS.EXE

    Original size (10.06.2000) =    342.560 bytes   **
                  (17.07.2003) =    385.120 bytes
                  (09.09.2003) =    396.928 bytes
                  (25.04.2005) =    407.344 bytes
                  (10.02.2007) =    410.944 bytes
                  (13.08.2010) =    413.280 bytes
                  (28.11.2017) =    415.664 bytes (147kb compressed)
                  (28.03.2018) =    416.832 bytes (132kb compressed)
                  (29.10.2020) =    432.640 bytes (->  136.724)
                  (02.09.2022) =    462.752 bytes (161kb)
                  (20.06.2023) =    486.032 bytes (167kb)

    Compressors (always newest versions, used on the 342 KB executable **)
        UPX --lzma                      1?????  (used)
        UPX -9                          114964
        UPX                             116349
        wwpack 3.05                     133588
        Compack 5.1                     140330
        Ainexe                          142627
        AVPack                          145527
        Diet                            147731
        Pklite 2.01                     150024
        LzEXE                           152456

# Computer Viruses and Malware - A Short Overview

A computer virus is a piece of code (software) that is installed on a computer either by a hacker, by another compromised computer (replication), malicious attachments/mails or a website (drive-by infection). It performs functions that the computer owner does not authorize and does not want.

Viruses are sometimes also referred to as malware. This is usually where they have adverse effects on the computer user, such as logging each keystroke (through a keylogger), audio recording or snapshots of each screen.

Such infection can lead to identity theft, endangerment of bank or purchase card data or loss of confidential data. It is more likely to occur on home computers that are normally not as security managed as corporate computers.

## 1. Malware

Malware, or malicious software, is a generic term for a variety of malicious or intrusive software, including computer viruses, worms, Trojans, ransomware (ransoms), spyware, adware, scareware and other malicious programs. It can take the form of executable code, scripts, active content and other software. Malware is defined by its malicious intent, which violates the requirements of the computer user - and therefore does not include software that causes unintentional damage due to a defect.

Programs officially delivered by companies can be considered malware if they secretly violate the interests of the computer user.

## 2. (Computer) Virus

A computer virus is a type of malicious software program ("malware") that, when executed, replicates itself by modifying other computer programs and appending or inserting its own code. When this replication succeeds, the affected programs are then said to be "infected" with a computer virus.

The term "virus" is also commonly, but erroneously, used to refer to other types of malware. "Malware" encompasses computer viruses along with many other forms of malicious software, such as computer "worms", ransomware, spyware, adware, Trojan horses, keyloggers, rootkits, bootkits, malicious Browser Helper Object (BHOs) and other malicious software. The majority of active malware threats are actually Trojan horse programs or computer worms rather than classic computer viruses.

Roughly you can distinguished between - Memory resident (fast) infecting viruses and - Direct action viruses

### 2.1. Direct Action Viruses

Direct action viruses are a type of malware that infect individual files on a computer, rather than the boot sector or Master Boot Record (MBR). They are called "direct action" viruses because they are executed each time a specific file is opened or executed, which allows the virus to infect other files on the computer.

Some of the simpler computer viruses do not actively manifest themselves in computer memory. The very first file infector viruses on the IBM PC, such as Virdem and Vienna, belong to this category. As a rule, direct viruses do not spread quickly and are not easily spread in the wild.

Direct action viruses load themselves into computer memory with the host program. Once they have taken control, they search for new objects to infect by searching for new files. For this very reason, one of the most common types of computer viruses is the direct action infector. This type of virus can be created relatively easily by the attacker in binary or scripting languages on a variety of platforms.

Direct action viruses typically use a FindFirst, FindNext sequence to search for a number of victim applications to attack. Typically, such viruses only infect a few files when executed, but some viruses infect everything at once, enumerating all the directories for victims.

Direct action viruses typically spread by attaching themselves to executable files, such as .exe, .com, or .bat files. When an infected file is executed, the virus infects other files on the computer and may also cause other malicious activity.

### 2.2. (Computer) Boot Virus

Boot viruses are the oldest known computer viruses. They were the most common type of virus until 1995, but are now extinct. Today, there are almost no boot sector viruses anymore because BIOS and operating systems usually have well-functioning software or hardware protection.

A boot virus is a computer virus that becomes active when the computer starts (boots) before the operating system (DOS, Linux or Windows) is fully loaded. Boot sector viruses take advantage of the fact that the boot sector is always loaded first. On floppy disks, the virus is at least partially in the boot sector, so even floppy disks with no files on them can be infected. On hard disks, the virus infects the master boot record (MBR) or logical boot sector.

A boot sector virus infects the boot sector of floppy disks and the master boot record (MBR) of a hard drive. The boot sector is the first physical part of a floppy disk and is a sector (512 bytes). The boot sector is used by boot floppies to boot from the floppy. When a user tries to boot from an infected boot floppy, or leaves an infected floppy in the floppy drive when the computer starts up, the BIOS accesses this sector and executes it with the appropriate BIOS boot setting. The virus then attempts to infect the hard disk’s MBR every time the computer is started. When an infected computer is started, the MBR, which is normally responsible for recognising the different partitions on the hard drive, is loaded. Once loaded, the virus remains in memory and monitors access to floppy disks. When a floppy disc is inserted into a computer infected with a boot sector virus, the virus infects the boot sector of the floppy disc.

Known boot viruses include the Form virus, Parity Boot and Boot-437.

### 2.3. Multipartite Virus

A multipartite virus is a computer virus that infects and spreads in multiple ways. The term was introduced to describe the first viruses that included DOS executable files and PC BIOS boot sector virus code, where both parts are viral themselves. Prior to the discovery of the first of these, viruses were categorized as either file infectors or boot infectors. Because of the multiple vectors for the spread of infection, these viruses could spread faster than a boot or file infector alone.

The first virus that infected COM files and boot sectors, Ghostball (more a dropper than a real multipartite virus), was discovered by Fridrik Skulason in October 1989. Another early example of a multi-part virus was Flip, Frodo, Delwin and Tequila. Tequila for example could infect both DOS EXE files and the MBR (master boot sector) of hard disks.

## 3. Trojan horses

A Trojan horse is a program that does something undocumented which the programmer intended, but that users would not accept if they knew about it. By some definitions, a virus is a particular case of a Trojan horse, namely, one which is able to spread to other programs (i.e., it turns them into Trojans too). According to others, a virus that does not do any deliberate damage (other than merely replicating) is not a Trojan. Finally, despite the definitions, many people use the term "Trojan" to refer only to a non-replicating malicious program.

## 4. Ramsomware

Ransomware is a particularly invasive form of malware that hijacks a victim’s data or device and holds it hostage (or makes false claims of illegal activity, pornography use, or suggests a system is already infected with viruses) until a sum of money is paid to secure its release. Ransomware has been around since about 1989, in the form of the DOS-AIDS Trojan (also known as PC Cyborg), which encrypted files on a hard drive and then demanded a payment of $189 to unlock them. The ransom is usually paid nowadays in cryptocurrencies such as bitcoin, monero, etc., as this allows anonymity and is difficult to trace. Attackers may also set a deadline for payment, threatening to delete or release the encrypted data and files if the ransom is not paid; this deadline is set to limit the response time and force the victim to choose the payment option. Ransomware has become a significant and global threat in recent years. It is important to note that paying the ransom is no guarantee that the victim’s data and system access will be restored or that sensitive data will not be leaked. Some attackers do not even provide the key or demand additional payments. According to Statista, only 54 per cent of organisations regained access to their data or systems after the first payment in 2021. Paying the ransom also encourages attackers to continue their malicious activities. In addition, the vulnerability still exists and can be exploited by another criminal group.

What are the steps in a ransomware attack? This depends on the level of sophistication. In most cases, the process is automated, but in some cases targeting large organisations, criminal groups will spend more time preparing to ensure they can successfully force the organisation to pay.

- Gaining access - A ransomware attack usually starts with the attacker gaining access to the victim’s computer or network through methods such as phishing emails, downloading infected software or exploiting network vulnerabilities.

- Spread - Once the attacker has access to a system on the internal network, they will attempt to spread the malware. In simple attacks, propagation depends on the sophistication of the malware and is automatic. In more targeted attacks, the malware goes home and leaves the attacker looking for ways to spread further and take control of more systems.

- Emergence and hostage taking - When the algorithm deems it appropriate, in the case of an automated attack or a criminal organisation, the systems are blocked and the data encrypted. In most cases, a message appears on some of the victim’s computers demanding a ransom to restore access to the data and/or systems.

## 5. Malicious Mining Software (Crypto-Miner)

Starting in 2018 Malware authors are increasingly relying on malicious mining software. This year for the first time there have been more infections of this type than with ransomware. More and more online criminals seem to turn their backs on ransomware and rely on crypto-miner. They secretly dig crypto money on infected computers - Monero is particularly popular. This is obviously extremely lucrative, as the latest figures show.

Reasons for the turnaround? If a ransomware/Trojan strikes and encrypts data from victims, they usually have to pay a ransom in the form of bitcoins. This is an obstacle that not every victim can or will take. Crypto-miner, on the other hand, only needs to infect computers. Afterwards, they dig in secret without any sacrifices and make silently sure that they bring the authors big profits - and not too short when you look at the exploding prices of different crypto currencies.

Nowadays even commercial antivirus software tries to use the user computer when idle for mining. So this kind of software is both a malware scanner and malware itself :-(

## 6. Greyware

Grayware (or greyware) is a general term sometimes used as a classification for applications that behave in a way that is annoying or unwanted, but less serious or problematic than malware. Grayware includes spyware, adware, dialers, joke programs, remote access tools and any other unwanted files and programs other than viruses that are designed to affect the performance of computers. The term has been in use since at least September 2004.

Grayware refers to applications or files that are not classified as viruses or Trojans, but can still affect the performance of computers on the user’s network and pose significant security risks to the user’s business. Grayware often performs a number of unwanted actions, such as annoying users with pop-up windows, tracking user habits and unnecessarily exposing the computer to attacks.

### 6.1. Scam

"Scam is a term used to describe a fraudulent scheme or deception in which someone is tricked into giving away money or personal information. Scams can take many different forms, such as phishing scams, investment scams, lottery scams and technical support scams, to name a few.

Phishing scams are attempts to trick people into revealing sensitive information, such as passwords or credit card numbers, by posing as a trustworthy entity. Investment scams persuade people to invest money in a bogus business or financial scheme with the promise of high returns. Lottery scams are messages informing people that they have won a large sum of money in a lottery, but asking them to pay a small fee or provide personal information to claim the prize. Tech support scams are attempts to trick people into paying for unnecessary computer support services by pretending to be from a reputable tech company.

Scammers often use persuasion and urgency to get people to hand over money or personal information. It is important to be wary of unsolicited messages or offers, and to independently verify the legitimacy of any request for personal information or money. You can protect yourself against fraud by being aware of common scams, being wary of unsolicited messages or offers, and never giving out personal information or money without verifying the identity of the recipient.

### 6.2. Adware

Adware is software that displays advertising banners in web browsers such as Chrome, Internet Explorer and Mozilla Firefox. Although it is not classified as malware, many users find adware invasive. Adware programs often have undesirable effects on a system, such as annoying pop-up ads and general degradation of network connection or system performance. Adware programs are usually installed as separate programs bundled with certain free software from websites. Many users inadvertently agree to install adware by accepting the End User License Agreement (EULA) of the free software. Adware is also often installed together with spyware programs. Both programs benefit from each other’s features - spyware programs profile users' Internet behavior, while adware programs display targeted advertisements that correspond to the collected user profile.

### 6.3. Spyware

Spyware is a type of computer virus that hides on your computer or mobile device, records your private data and sends that information back to whoever created it or monitors it. The tricky thing about spyware, and what separates it from the growing threat of ransomware is the fact that, spyware is designed to both install discretely and operate silently in the background.

Spyware is software that installs components on a computer to record browsing habits (primarily for marketing purposes). Spyware sends this information to its creator or to other interested parties when the computer is online. Spyware is often downloaded along with other components that are referred to as "free downloads" or "freeware" without informing the user about their existence or asking for permission to install them. The information that spyware components collect can include user’s keystrokes (keylogging), which means that private information such as login names, passwords and credit card numbers can be stolen. Spyware collects data, such as account names, passwords, credit card numbers and other confidential information, and transmits it to third parties.

## 7. Backdoors

A point of access to a hidden program/system. Backdoors are usually intentionally created by a programmer for debugging or maintenance purposes, but if compromised, they can pose a security risk to unauthorized users or software, allowing access and causing damage. Malware often installs Backdoors on compromised systems!

## 8. Botnets

A bot is a programs that run automated tasks over the Internet. Botnets are collection of bots that run autonomously and automatically. Typically they perform repetitive tasks at a much higher rate than a human is capable of. They can be used for malicious purposes, such as denial of service attacks or infecting other computers. An infected computer is called a bot or zombie.

## 9. Macro viruses

A macro is a piece of code that can be embedded in a data file. A macro virus is thus a virus that exists as a macro attached to a data file. In most respects, macro viruses are like all other viruses. The main difference is that they are attached to data files (i.e., documents) rather than executable programs. Document-based viruses are, and will likely continue to be, more prevalent than any other type of virus.

## 10. Worms

Worms are very similar to viruses in that they are computer programs that replicate functional copies of themselves (usually to other computer systems via network connections) and often, but not always, contain some functionality that will interfere with the normal use of a computer or a program. Unlike viruses, however, worms exist as separate entities; they do not attach themselves to other files or programs. Because of their similarity to viruses, worms also are often referred to as viruses.

## 11. Protestware

In March 2022, a developer of node-ipc was caught adding malicious code to the popular open source package that deleted files on computers in Russia and Belarus. This was part of a protest that angered many users and raised concerns about the security of free and open source software. The node-ipc update is just one example of what some researchers call protestware. Most protest programs related to the Russian invasion of Ukraine simply display anti-war and pro-Ukrainian messages. However, in at least one project, virus-like code was added that aimed to cripple computers in Russia and Belarus. This led to criticism and accusations of causing collateral damage. But there are also examples of protest in the open source scene. Observers of the scene so far found about two dozen software projects that inserted "code against war."

Open-source programs can be modified and viewed by anyone, making them more transparent - and, at least in this case, more vulnerable to sabotage. The protestware event highlights some of the risks that arise when legions of volunteer developers create the code that is critical to running hundreds or thousands of other applications. Some open source software automatically downloads and integrates new versions, and even for those that don’t, the vast amount of code often makes manual review infeasible. This means that an update by a single person can mess up an untold number of downstream applications. In that sense, this can be considered a "game changer."

Russia’s largest bank has asked its customers to stop updating its software because it is under threat from "protestware". In response to the threat, Russian state-owned bank Sberbank even advised its Russian customers to manually check the source code of the software they need - a security measure that is not feasible for most users. "We urge users to stop updating software and developers to tighten monitoring when using external code," Sberbank said, according to Russian media and cybersecurity firms.

## 12. Stealth viruses

What is a stealth virus? A stealth virus is one that, while active, hides the modifications it has made to files or boot records. It usually achieves this by monitoring the system functions used to read files or sectors from storage media and forging the results of calls to such functions. This means that programs that try to read infected files or sectors see the original, uninfected form instead of the actual, infected form. Thus the virus’s modifications may go undetected by antivirus programs. However, in order to do this, the virus must be resident in memory when the antivirus program is executed, and the antivirus program may be able to detect its presence.

The very first DOS virus, Brain, a boot-sector infector for example monitored physical disk input/output and redirected any attempt to read a Brain-infected boot sector to the disk area where the original boot sector was stored.

### 12.1. File stealth viruses

In addition to hiding the boot information, DOS file stealth viruses attack .com and .exe files when opened or copied, and hide the file size changes from the DIR command. The major problem arises when you try to use the CHKDSK/F command and there appears to be a difference in the reported files size and the apparent size. CHKDSK assumes this is the result of some cross-linked files and attempts to repair the damage. The result is the destruction of the files involved.

### 12.2. Full stealth viruses

With a full stealth virus, all normal calls to file locations are cached, while the virus subtracts its own length so that the system appears clean.

### 12.3. Countermeasures against Stealth Viruses?

You need a clean system so that no virus is present to distort the results of system status checks. Thus you should start the system from a trusted, clean, bootable diskette before you attempt any virus checking.

## 13. Encryption

One method of evading malware detection is to use simple encryption to encipher (encode) the body of the malware, leaving only the encryption module and a static cryptographic key in clear text which does not change from one infection to the next.

### 13.1. What is a polymorphic virus?

A polymorphic virus is one that produces varied but operational copies of itself. This strategy assumes that virus scanners will not be able to detect all instances of the virus. One method of evading scan-string driven virus detectors is self-encryption with a variable key. Polymorphic code was the first technique that posed a serious threat to virus scanners.

More sophisticated polymorphic viruses (e.g., V2P6) vary the sequences of instructions in their variants by interspersing the decryption instructions with "noise" instructions (e.g., a No OPeration instruction (NOP), or an instruction to load a currently unused register with an arbitrary value), by interchanging mutually independent instructions, or even by using various instruction sequences with identical net effects (e.g., Subtract A from A, and Move 0 to A). A simple-minded, scan-string based virus scanner would not be able to reliably identify all variants of this sort of virus; in this case, a sophisticated scanning engine has to be constructed after thorough research into the particular virus.

One of the most sophisticated forms of polymorphism used so far is the Mutation Engine (MtE) or the Trident Polymorph Engine (TPE), which comes in the form of an object module. With such mutation engines, any virus can be made polymorphic by adding certain (API) calls to its assembler source code and linking to the mutation-engine and provided random-number generator modules.

The advent of polymorphic viruses has rendered virus scanning an increasingly difficult and expensive endeavor; adding more and more search strings to simple scanners will not adequately deal with these viruses.

## 14. What is an armored virus?

Armored viruses use special tricks to make the tracing, disassembling, and understanding of their code more difficult. A good example is the Whale virus. An armored virus uses various techniques to evade detection, such as encrypting its code, obfuscating its code, and using anti-debugging and anti-tampering methods.

Armored viruses pose a serious threat because they can be used to perform malicious activities such as stealing sensitive information, altering or corrupting data, and slowing performance without being detected. They can also be used as part of more complex attacks, such as advanced persistent threats (APTs), to maintain a foothold on a target network over an extended period of time.

## 15. What is Phishing/Vishing?

Phishing and vishing are types of scams used to steal sensitive information such as passwords, credit card numbers and other personal data.

Phishing is a type of scam that tricks people into providing sensitive information through fake emails or websites that appear to be from a reputable source, such as a bank or a well-known company. The goal of phishing scams is to trick people into revealing personal information, such as passwords or credit card numbers, by posing as a trustworthy entity.

Vishing, short for voice phishing, is a type of phishing scam where people are tricked into revealing sensitive information over the phone. In vishing scams, scammers often pretend to be from a bank, government agency or technology company and use persuasive techniques to get people to reveal sensitive information.

Both phishing and vishing scams are becoming increasingly sophisticated and it is important to be wary of unsolicited emails or phone calls. To protect yourself from these types of scams, never provide sensitive information in response to an unsolicited request and independently verify the identity of the recipient before providing any personal information.

## 16. Best Practices

Ransomware attacks can be extremely damaging and complex, and the timeframe for action is very limited. The best way to deal with them is to avoid them in the first place, and use mechanisms to prevent and mitigate their impact. The best way to prevent a malware attack is to follow good operational and security practices, such as

- Keep all software and operating systems up to date.

- Use anti-virus and anti-malware software on desktop systems.

- Regularly scan for vulnerabilities and comply with security policies, the key is to do this regularly.

- The best way to do this is to automate it so that it does not become a problem and can be integrated as part of the deployment process.

- Ensure that the software supply chain is properly secured. From an attacker’s perspective, attacking the supply chain may be the easiest way to reach most, if not all, of an organisation’s systems.

- Implement proactive measures and adopt a zero-trust policy. This applies to containers as well as traditional environments.

- Implement password validation best practices, such as avoiding common words and using long phrases that are easier for humans to remember but harder for machines to crack.

- Educate staff on basic security principles, such as being wary of suspicious emails, recognising suspicious links and managing data to avoid storing critical data in unsecured locations.

- Perform regular backups and always keep a cold backup in a separate physical location with no network access. Ensure that recovery procedures are tested regularly.

- Automate the provisioning of your infrastructure so that you can restore your systems quickly - time is money.

- Have a disaster recovery plan in place and ensure it is tested regularly.

## 17. Links / Pointers

https://en.wikipedia.org/wiki/Timeline_of_computer_viruses_and_worms

## 18. Some very old DOS viruses that were very widespread in the past

### 18.1. Cascade

Cascade virus (also known as Herbstlaub in Germany) is a well-known DOS computer virus that is a memory-resident virus written in assembly language. Cascade was widely spread in the 1980s and early 1990s. It infected DOS .COM files and caused the text on the screen to cascade down and form a pile at the bottom of the screen. It was notable for the fact that it used an encryption algorithm to avoid detection. However, it could be seen that the size of the infected files increased by 1701 or 1704 bytes. In response, IBM developed its own anti-virus software.

When a file infected with Cascade is introduced into a system and executed, the virus checks the BIOS for the string "COPR. IBM", an IBM copyright notice in the BIOS. If it finds the string, it tries to stop there, but fails, and the virus becomes memory resident. Every time a .COM file is executed, the virus starts infecting it. It replaces the first three bytes of the new host file with code that references the virus code. The virus places the original first three bytes of the host into its own code.

Cascade’s payload is executed when an infected file is executed between October 1 and December 31, 1988. It causes characters on a DOS screen to randomly drop down in a pile of numbers and letters. Variants can also cause noise.

The virus has a number of variants. Cascade-17Y4, which is believed to have originated in Yugoslavia, is almost identical to the most common 1704-byte variant. One byte has been changed, probably by a random "mutation". However, this has resulted in a "bug" in the virus. Another mutated variant is also known - it infects the same file over and over again.

### 18.2. Jerusalem

Jerusalem is a DOS virus which was first detected in Jerusalem in October 1987. Its origin is uncertain, as it was thought to have originated in Israel, but evidence from 1991 suggests that it may have originated in Italy. As of 1993, Jerusalem was still in the wild and many variants had been created. The last reported case of Jerusalem was in 1995, almost 8 years after its discovery. The virus has gone by many names, some referring to its possible origin and its Friday the 13th payload date. Jerusalem was initially very common (for a virus at the time) and spawned a large number of variants. However, since the advent of Windows, these DOS interrupts are no longer used, so Jerusalem and its variants have become obsolete.

Once infected, the Jerusalem virus becomes memory resident (using 2kb of memory) and then infects every executable file that is run, except for COMMAND.COM. COM files grow by 1,813 bytes when infected by Jerusalem and are not re-infected. EXE files grow between 1,808 and 1,823 bytes each time they are infected. The virus re-infects .EXE files each time they are loaded until they are too large to load into memory. Some .EXE files are infected but do not grow because multiple overlays follow the real .EXE file in the same file. Sometimes .EXE files are infected by mistake, so that the programme fails to run when it is run.

The virus code itself hooks into interrupt processing and other low level DOS services. For example, code in the virus suppresses the printing of console messages if, for example, the virus is not able to infect a file on a read-only device such as a floppy disk. One of the clues that a computer is infected is the mis-capitalization of the well-known message "Bad command or file name" as "Bad Command or file name".

The program contains one destructive payload that is set to go off on Friday the 13th, all years but not in 1987. On that date, the virus deletes every program file that was executed. Jerusalem is also known as BlackBox because of a black box it displays during the payload sequence. If the system is in text mode, Jerusalem creates a small black rectangle from row 5, column 5 to row 16, column 16. The rectangle is scrolled up by two lines.

As a result of the virus hooking into the low-level timer interrupt, PC-XT systems slow down to one fifth of their normal speeds 30 minutes after the virus has installed itself. The slowdown is less noticeable on faster machines. The virus contains code that enters a processing loop each time the processor’s timer tick is activated.

Symptoms also include spontaneous disconnection of workstations from networks and creation of large printer spooling files. Disconnections occur since Jerusalem uses the interrupt 21h low-level DOS functions that Novell Netware and other networking implementations required to hook into the file system.

Variants

Over the years that Jerusalem spread, many virus coders created variants of the virus, making Jerusalem one of the largest families of viruses ever created. It even includes many sub-variants and a few sub-sub-variants. Most variants are unimaginative, simply changing the payload date, text displayed or even nothing at all. Some variants contain fixes for the bugs of the original.

    Jerusalem.1013 Jerusalem.1024 Jerusalem.1234 Jerusalem.1237 Jerusalem.1238
    Jerusalem.1241 Jerusalem.1244 Jerusalem.1264 Jerusalem.1291 Jerusalem.1329
    Jerusalem.1347 Jerusalem.1348 Jerusalem.1349 Jerusalem.1353 Jerusalem.1356
    Jerusalem.1361 Jerusalem.1363 Jerusalem.1364 Jerusalem.1390 Jerusalem.1399
    Jerusalem.1408 Jerusalem.1427 Jerusalem.1446 Jerusalem.1448 Jerusalem.1455
    Jerusalem.1459 Jerusalem.1477 Jerusalem.1478 Jerusalem.1487 Jerusalem.1488
    Jerusalem.1489 Jerusalem.1500 Jerusalem.1503 Jerusalem.1504 Jerusalem.1511
    Jerusalem.1518 Jerusalem.1521 Jerusalem.1522 Jerusalem.1523 Jerusalem.1524
    Jerusalem.1525 Jerusalem.1526 Jerusalem.1530 Jerusalem.1533 Jerusalem.1536
    Jerusalem.1548 Jerusalem.1552 Jerusalem.1558 Jerusalem.1562 Jerusalem.1568
    Jerusalem.1570 Jerusalem.1587 Jerusalem.1589 Jerusalem.1591 Jerusalem.1596
    Jerusalem.1598 Jerusalem.1605 Jerusalem.1607 Jerusalem.1624 Jerusalem.1631
    Jerusalem.1639 Jerusalem.1640 Jerusalem.1653 Jerusalem.1664 Jerusalem.1682
    Jerusalem.1692 Jerusalem.1715 Jerusalem.1716 Jerusalem.1720 Jerusalem.1721
    Jerusalem.1728 Jerusalem.1733 Jerusalem.1735 Jerusalem.1747 Jerusalem.1756
    Jerusalem.1765 Jerusalem.1767 Jerusalem.1768 Jerusalem.1783 Jerusalem.1792
    Jerusalem.1807 Jerusalem.1808 Jerusalem.1813 Jerusalem.1824 Jerusalem.1845
    Jerusalem.1884 Jerusalem.1888 Jerusalem.1899 Jerusalem.1960 Jerusalem.1968
    Jerusalem.1970 Jerusalem.1975 Jerusalem.1984 Jerusalem.1991 Jerusalem.2000
    Jerusalem.2012 Jerusalem.2027 Jerusalem.2053 Jerusalem.2064 Jerusalem.2080
    Jerusalem.2082 Jerusalem.2083 Jerusalem.2116 Jerusalem.2126 Jerusalem.2128
    Jerusalem.2132 Jerusalem.2187 Jerusalem.2208 Jerusalem.2223 Jerusalem.2224
    Jerusalem.2272 Jerusalem.2291 Jerusalem.2350 Jerusalem.2358 Jerusalem.2368
    Jerusalem.2389 Jerusalem.2437 Jerusalem.2465 Jerusalem.2472 Jerusalem.2490
    Jerusalem.2576 Jerusalem.2758 Jerusalem.2880 Jerusalem.2886 Jerusalem.3887
    Jerusalem.4112 Jerusalem.5120 Jerusalem.641 Jerusalem.662 Jerusalem.679
    Jerusalem.878 Jerusalem.880 Jerusalem.986 Jerusalem.A Jerusalem.CVEX
    Jerusalem.Curse Jerusalem.June11_T3Scan Jerusalem.Plastique
    Jerusalem.Roger Jerusalem.a Jerusalem.com Jerusalem.sURIV_3

### 18.3. Stoned

Stoned is a very large family of boot sector viruses on the DOS platform that started in early 1988. Prominent members of this family include the infamous Michelangelo virus, which caused great panic in the early 1990s, and the Angelina virus from 1994, which resurfaced on infected laptops in 2007. The Stoned virus was allegedly programmed by a student at the University of Wellington in New Zealand.

When the computer boots from an infected hard drive, Stoned becomes resident in memory. When booting from a disk other than the hard disk, it checks the master boot record of the hard disk and infects it if it is clean. When infecting a floppy disk, Stoned moves the master boot record to sector 11 and places itself in sector 0. When infecting the hard disk, it moves the master boot record to page 0, cyl. 0, sector 7 and places itself in page 0, cyl. 0, sector 1. It infects only 360-kilobyte 5.25-inch floppy disks and hard disks in the original variant.

Once in memory, the virus infects the master boot records of all accessed floppy disks. It cannot reinfect the hard disk. Even if the virus is removed from the Master Boot Record while it is in memory, it will not attempt to reinfect the hard disk.

There is a 1 in 8 chance that Stoned will release its payload while booting, causing the infected computer to beep and display the message:

    Your PC is now stoned! LEGALIZE MARIJUANA!

Michelangelo

Michelangelo was the first computer virus to attract much media attention. It caused a great deal of panic, but very little actual damage. Michaelangelo infected only a few thousand computers, making it an example of media hype.

The hype began in January 1992, when one computer manufacturer accidentally shipped 500 computers infected with the virus, and on the same day another announced that it would ship computers with anti-virus software pre-installed. This coincidence aroused the interest of the press. United Press International interviewed the International Partnership Against Computer Terrorism and the president of the antivirus company, John McAfee, and reported that hundreds of thousands of computers may be destroyed by the virus. Data recovery consultant Martin Tibor captured the interest of the press with quotes such as "I find virus disasters everywhere" and "I see victims of viruses all the time."

In the weeks leading up to the payload’s release date, newspapers began reporting on the "local impact". Although some news outlets reported on the hysteria rather than the virus, few did anything to stop the hysteria (e.g., by talking to real experts). A significant number of computer users bought antivirus software.

/* End of Document */

## 19. Copyright

©opyright by

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      Dipl.-Ing. Ralph Roth              full address, FAX and PGP keys.
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## 20. End

End of the documentation! Thank you for reading it. Bye!